Recent content by Ghost Repeater

Homework Statement This is just a question about a question in Serway & Jewett's "Physics for Scientists and Engineers 3rd Ed". It's Objective Question 3 from Chapter 18, building on Example 18.1 from the text. Two identical loudspeakers placed 3.00 m apart are driven by the same oscillator...

Well, that makes sense! Negligible is negligible, after all, ha ha. Thanks for the reply.

Homework Statement .[/B] For a certain type of steel, stress is always proportional to strain with Young's modulus 20 x 10^10 N/m^2. The steel has density 7.86 x 10^3 kg/m^3. A rod 80.0 cm long, made of this steel, is fired at 12.0 m/s straight at a very hard wall. a) The speed of a...

This is not a technical question. I'd like to have a more conceptual discussion about what - if anything - gauge invariance tells us about reality. If we could, please try to keep the discussion at the level of undergrad or beginning grad. To focus my questions and keep things elementary, I'd...

Ah, that's it. The normal force then would be applied at the pivot point and so its torque would vanish. Correct?

Homework Statement A block of uniform density experiences a force F to the right, applied 5/3 m from the bottom of the block. The block is 2 m high and 1 m wide. Take the pivot point to be the point at the bottom right of the block. Find the value of the force that is just able to tip the box...

Thanks for your reply! So using ##S = kln(\Omega)## seems to still leave me in a quandary, because for the macropartition ##0:6## (where object A has no bits of energy, object B has all 6), ##\Omega_{A} = 0## and therefore ##\Omega_{AB} = \Omega_{A} \Omega_{B} = 0##, which gives me an...

I may be overthinking it, since I know the problem is supposed to be preparation for modifying these Newtonian concepts for SR later on. I just have a 'so what?' feeling about this 'result', perhaps because I am not familiar enough with relativity. Is it surprising that the change in KE should...

Thanks for pointing our my calculation error there. So here's a summary of what I've got so far. Ground Frame: $$KE_i = 2 (\frac{1}{2}mv_i^2) = mv_i^2$$ (I changed notation here a bit, using ##v_i## to represent initial speed in the ground frame.) $$KE_f = \frac{1}{2}(2m)v_f^2 = 0$$...

Ha ha, dumb mistake. Sorry. Yes, so the initial momentum in the object frame is $$p'_i = m(2v) = 2mv$$ Since momentum is conserved, this must also be the final momentum, so $$p'_f = 2mv = (2m)v'_f$$ from which it follows that $$v'_f = v$$ And since v'i = 2v, so v = (1/2)v'i, so $$v'_f =...

Homework Statement [This problem is part of a preparation for modifying the concepts involved in special relativity.] Two cars collide and lock together. They are each a mass of 800 kg and were traveling at a steady 20 m/s in opposite directions prior to collision. a) What's the kinetic...

Homework Statement [/B] Strap in, this one's kind of long. (This problem is from 'Six Ideas That Shaped Physics, Unit T' by Thomas A Moore, 2nd edition. Problem T6R2.) Imagine that aliens deliver into your hands two identical objects made of substances whose multiplicities increase linearly...

I'm sorry to be obtuse about this, but that seems to be precisely NOT how they are using it in these cases. Bloomfield specifically says BOTH that the object 'looks black in the infrared' AND that it 'glows brightly in the infrared'. So he is not using black in the same sense as you are when you...

So in what sense, precisely, does a room temperature object 'look black' to someone who can perceive IR? If it's emitting IR, then how can someone who perceives IR not perceive it to have a color corresponding to whatever IR wavelength its emitting at? And if black surfaces emit light, what is...

Thank you for your reply. But I'm still confused. Bloomfield makes two claims: 1) An object at room temperature would look black to someone perceiving infrared. 2) An object at room temperature glows brightly in the infrared spectrum. I still don't see how these two statements can be made...